1. Field of the Invention
Aspects of the present invention relate to an image forming apparatus, and more particularly, to an image forming apparatus having an improved printing medium feeding apparatus.
2. Description of the Related Art
In general, an image forming apparatus prints image data on a printing medium, such as a sheet of paper, a transparency sheet, etc., according to a printing signal transmitted from a host apparatus. The image forming apparatus may perform a variety of functions, such as a scanning function to scan a document and generate image data corresponding to the document, an e-mail transmitting function to transmit image data to an e-mail account through an e-mail server, a facsimile transmitting function to transmit image data of a document to an external facsimile machine through a modem, and a copying function to copy image data of a document onto a printing medium or a plurality of printing media. Recently, image forming apparatuses have been designed as multifunctional devices which perform two or more of the above-described functions simultaneously for the convenience of a user or users.
In general, the image forming apparatus includes a feeding part to feed the printing medium onto a feeding path, an image forming part to apply developer or ink on the printing medium to form an image, and a discharging part to discharge the printing medium outside of the image forming apparatus.
FIG. 1A is a schematic view illustrating a configuration of a conventional image forming apparatus 10. As shown in FIG. 1A, the conventional image forming apparatus 10 includes a feeding cassette 20 in which sheets of printing media are stored, a pick-up roller 40 which picks up individual sheets of the printing media from the feeding cassette 20, a paper aligning roller part 50 which aligns a leading edge of a printing medium picked up by the pick-up roller 40 and transfers the aligned printing medium to an image forming part 60, and a casing 70.
As shown in FIG. 1B, the paper aligning roller part 50 includes a pair of transferring rollers 51 and 53 which transfer the printing medium picked up by the pick-up roller 40 to the image forming part 60, and a shutter 55 which is coupled to a rotational shaft with the transferring roller 51. The shutter 55 has a protruding part 55a which rotates according to pressure from the printing medium picked up by the pick-up roller 40 and moving along a feeding path. The shutter 55 contacts the printing medium as the printing medium is being transferred to the image forming part 60 and aligns a leading edge of the printing medium before the transferring rollers 51 and 53 contact the printing medium. The shutter 55 applies a repulsive force to the printing medium to uniformly align the leading edge of the printing medium before the pressure of the moving printing medium exceeds a reference pressure.
The shutter 55 rotates at a predetermined angle if the leading edge of the printing medium is uniformly aligned and the pressure applied to the shutter 55 by the leading edge of the moving printing medium exceeds the reference pressure. Accordingly, the printing medium enters between the transferring rollers 51 and 53 with an aligned leading edge.
However, in the conventional image forming apparatus 10 having the paper aligning roller part 50 described above and shown in FIG. 1B, the printing medium does not always press the protruding part 55a at the same angle. Instead, the printing medium may press the shutter 55 at a center angle indicated by the arrow “c”, an external angle in a direction indicated by the arrow “a” pointing away from the transferring roller 51, an internal angle in a direction indicated by the arrow “b” pointing towards the transferring roller 51, or another angle.
If the printing medium presses the shutter 55 at a center angle “c”, the shutter 55 rotates and properly aligns the leading edge of the printing medium when the pressure applied by the moving printing medium exceeds the reference pressure. However, the shutter 55 may rotate even when a smaller pressure than the reference pressure is applied by the moving printing medium when the printing medium presses the shutter 55 at the external angle “a”. In this case, a problem occurs when the printing medium enters between the transferring rollers 51 and 53 before the leading edge of the printing medium is aligned, because the printing medium moves to the image forming part 60 in an unaligned state. Accordingly, when the unaligned leading edge of the printing medium is transferred to the image forming part 60, printing quality decreases.
Also, if the printing medium presses the internal side of the shutter 55 at the internal angle represented by the arrow “b” in FIG. 1B, the shutter 55 does not rotate at all. In this case, the paper aligning roller part 50 fails to transfer the printing medium to the image forming part 60, resulting in a paper jam even if the printing medium contacts the shutter 55 with a larger pressure than the reference pressure.
Meanwhile, the above-described problems become even more serious if the image forming apparatus 10 has a plurality of feeding parts to transfer multiple sheets of the printing media from different directions and angles. Specifically, the range of angles at which the sheets of the printing media contact the shutter 55 further increases, resulting in a further decrease in printing quality and more paper jams.